One of the problems encountered with piezoelectric resonators are the unwanted spurious responses, clustered around the fundamental and overtone responses.
The exact level of spurious (unwanted) responses is difficult to predict in advance, before the physical piezoelectric device is actually built. However, the general relationship of the spur response level to different device parameters is well known. The theory relating the piezoelectric device physical properties to the presence and level of spurious responses, is known as the Energy Trapping Theory. According to the theory, one of the parameters strongly affecting the existence of spurious responses, is so-called "mass loading". In a simple case, this parameter can be related to the actual mass of the metal electrode of the piezoelectric device. More precisely, the factor of primary importance is the difference between the mass per unit area of the electroded region and the mass per unit area of the unelectroded region of the device. In many commercial devices, this parameter is controlled by the choice of electrode metal and the thickness of the electrode.
Controlling the spurious responses becomes even more critical with overtone devices. The existence of spurious responses in overtone devices can be minimized when lightweight metal, such as aluminum, is used and the electrode thickness is kept to a minimum, but which is still sufficient to maintain electrical conductivity.
This invention relates to reducing the mass loading effect through an approach different from simply reducing the electrode mass.
There exists a need for an improved arrangement for fabricating piezoelectric resonators, such as quartz crystal blanks, in which unwanted spurious responses can be minimized.
A structure which helps minimize unwanted spurs in fundamental and overtone responses, would be considered an improvement in the art.